This invention teaches the use of inexpensive materials in web or sheet form and methods for fabricating same to provide substantial cost reductions in a solar ray collector assembly, especially solar concentrator assemblies which employ the use of curved focusing surfaces.
The use of parabolic reflector surfaces to direct solar rays to a focal point is old art, for example, U.S. Pat. No. 1,704,173.
Numerous other patents also relate the general principle of concentrating solar rays to a focal point, for example, parabolic shapes of U.S. Pat. Nos. 1,989,999; 2,688,922; 3,300,393; and 3,923,039.
While each of these teachings have modifications or adaptations for special use, a common feature of each is the use of a reflector plate having a rigid surface between supports placed at the terminal ends of the reflector surface, or the use of a flexible reflector supported by a continuous sub-member in order to prevent deflection (which causes misdirection of reflected rays and loss of efficiency). Although intermediate, upper convex supports can be used to prevent excessive deflection, these additional supports interfere with incoming solar rays and reduce total effectiveness.
U.S. Pat. No. 1,855,815 shows a parabolic reflector to focus rays on an axial, cylindrical, fluid-carrying tube and an arrangement to pivot the reflector about the tube axis. U.S. Pat. No. 1,946,184 shows the central tube with a concentric transparent outer tube which supports a parabolic reflector element about the central tube.
For many years, these prior art teachings were alone in describing the basic principle of reflection-concentration along a focal line until U.S. Pat. No. 3,847,136 taught a simplified construction using a flexible reflector surface placed on the top surface of a formed or molded plastic member (which has a semi-cylindrical upper concave contour) to reflect rays to an axial fluid-carrying heat transfer tube. The collector in U.S. Pat. No. 3,847,136 shows the combination of a stiff, self-supportive member and a flexible reflective surface placed within the concave trough of the self-supportive member, and also shows end supports with a pair of bearings to allow pivoting of the structure about the central tube. U.S. Pat. No. 3,847,136 shows a member made of foamed or expanded plastic and uses a monolithic, shaped member to obtain axial and transverse rigidity for reflective accuracy. This teaching requires a fairly heavy cross-section directly below the nadir of the curve to prevent transverse deflection, and substantial continuous longitudinal thickness to prevent axial deflection.
In order to reduce weight and costs of the reflector of the present invention, I use a novel construction whereby the reflective surface is shaped by supporting it by laminated or spaced segments made from inexpensive web or flat sheet materials. This invention does not claim the continuous contoured member as being self-supportive, but rather is directed to the use of a plurality of laminated or spaced-apart supportive members in combination with a supportive planar subsurface (or spaced apart supports) to overcome axial and transverse deflections.
This construction advantageously lends itself to parabolic shapes which have large apertures and minimizes material requirements between the nadir of the paraboloid and the substructure. The reflective surface substrate can also be selected from a wide range of semi-rigid to flexible materials, as, for example, light gauge metals sheets which require only intermittent parabolic shaped supporting members, thus reducing weight and cost. With large aperture reflective surfaces, higher concentration ratios become possible as long as high accuracy of the parabolic curve is maintained. The present invention teaches a unique combination of elements to achieve this, and also teaches a method for fabricating the concave parabolic supporting member continuously and with high accuracy.